1. Field of the Invention
The present invention relates to a single phase motor. In particular, this invention relates to a driving apparatus and a driving method for a single phase motor.
2. Description of the Related Art
Reference is made to FIGS. 1A˜1C, a driving apparatus for a single phase motor of the prior art is illustrated. FIGS. 1A and 1B are the block diagram of the driving apparatus for a single phase motor of the prior art. FIG. 1C is a timing chart of the signals in the driving apparatus for a single phase motor of the prior art. The driving apparatus of the prior art includes four driving transistors 102, 104, 108, 110, two recirculating diodes 112, 114, a single phase coil 106, a hall apparatus 116, a comparing circuit 118, an absolute value circuit 120, a detecting device 122, and a control circuit 132.
First, the hall apparatus 116 senses the rotating location of the single phase motor. This means that the hall apparatus 116 senses the variation of the magnetic poles located in the rotor to output a sine wave signal. Next, the comparing circuit 118 reshapes the sine wave signal outputted from the hall apparatus 116 into a square wave signal. The square wave signal is a current-switching signal. The absolute value circuit 120 compares the level of the sine wave signal with a reference value to output a timing signal to recirculate the driving current of the single phase coil 106. The comparing circuit 130 compares the charging/discharging voltage in a non-grounded terminal of the comparing capacitor 124 with the reference voltage VREF to determine whether the single phase motor is rotating or not. When the single phase motor is rotating, an “H” detecting signal is outputted. When the single phase motor is not rotating, an “L” detecting signal is outputted.
Finally, the control circuit 132 calculates the outputs of the comparing circuit 118 and the absolute value circuit 120 according to the output of the detecting device 122. When the detecting signal is “L”, the driving signals A1, B1, C1, and D1 are outputted. When the detecting signal is “H”, the driving signals A2, B2, C2, and D2 are outputted.
Because the sine wave signal outputted from the hall apparatus 116 has a 180 degrees phase difference between the black line and the dotted line, a zero cross point (a current-switching point of the driving current) exists.
When the driving signals A2 and D2 rise, the driving transistors 102 and 104 are conducted (ON-status). The direction of the driving current in the signal phase coil 106 is right while facing to paper. When the driving signal A2 descends, only the driving transistor 104 is conducted. The driving current counterclockwise circles along the recirculating path (represented by the dotted line) composed of the single phase coil 106, the driving transistor 104, and the recirculating diode 112, consumes and becomes zero. When the driving signal D2 also descends, the driving transistor 104 turns off on the zero cross point.
When the driving signals B2 and C2 rise, the driving transistors 108 and 110 are conducted (ON-status). The direction of the driving current in the signal phase coil 106 is left while facing to paper. When the driving signal C2 descends, only the driving transistor 110 is conducted. Therefore, the driving current counterclockwise circles along the recirculating path (represented by the dotted-dash line), consumes and becomes zero. When the driving signal B2 also descends, the driving transistor 110 turns off.
Reference is made to FIGS. 2A and 2B, which show a schematic diagram of part of a circuit of a driving apparatus for a single phase motor of the prior art, and a timing chart of the signals in the driving apparatus for a single phase motor of the prior art.
The transistors 2, and 4 provide the driving current to the single phase coil 6 in the right direction while facing to the paper via the driving signals A and D. The collector-base of the transistor 2, the single phase coil 6, and the collector-emitter of the transistor 4 are connected in series and are connected between the power Vcc and the grounding Vss. The transistors 8 and 10 provide the driving current to the single phase coil 6 in the left direction while facing to the paper via the driving signals C and B. The collector-emitter of the transistor 8, the single phase coil 6, and the collector-emitter of the transistor 10 are connected in series and are connected between the power Vcc and the grounding Vss. Therefore, the transistors 2, 4, and the transistors 8, 10 are individually on one of the ON and OFF statuses to change the direction of the driving current on the single phase coil 6 to make the single phase motor rotate.
However, the timing of the driving signals A, B, C, and D, merely shift a little, the driving current on the single phase coil 6 does not have a positive effect upon the slope redundant current. The direction of the driving current of the single phase coil 6 rapidly changes so that the single phase motor suffers some problems, including vibration, noise, and a heavy power consumption.